Lateral Variations in Foreland Flexure of a Rifted Continental Margin: The Aquitaine Basin (SW France)

Abstract

Rift inheritance can play a key role in foreland basin geometry and behavior. If the foreland basin initiates soon after rifting, thermal cooling can also contribute significantly to subsidence. We investigate the effects of crustal inheritance (Aptian‐Cenomanian rifting) on the evolution of the Campanian to middle Miocene flexural Aquitaine foreland basin, northern Pyrenees, France. Surface and subsurface data define rifted crustal geometry and postrift thermal subsidence. Analysis of Bouguer gravity anomalies coupled with flexural modeling constrains the lateral variations of elastic thickness, plate flexure, and controlling loads. The Aquitaine foreland is divided along‐strike into three sectors. The relative role of surface and subsurface (i.e., buried) loading varies along‐strike, and the elastic thickness values decrease from the northeast (25 km) to the southwest (7 km) where the plate is the most stretched. The eastern foreland crust was not rifted and underwent a simple flexural subsidence in response to orogenesis. The central sector was affected by crustal stretching. Here the basin is modeled by combining topographic and buried loads, with postrift thermal subsidence. In the western sector, the foreland basin was created mainly by postrift thermal subsidence. The eastern and central sectors are separated by the Eastern Crustal Lineament, which is one of a series of inherited transverse faults that segment the orogen.

Thermochronological Evidence of Early Orogenesis, Eastern Pyrenees, France

“…There is also no thermal signature of subduction preceding collision, as is the case in many orogens, because no true oceanic crust was formed before the onset of convergence (Clerc & Lagabrielle, 2014;Jammes et al, 2009;Lagabrielle et al, 2010;Lagabrielle & Bodinier, 2008;Masini et al, 2014;Tugend et al, 2014). On the other hand, the Aptian-Cenomanian rifting generated a major thermal pulse that had not reequilibrated before the onset of convergence some 10 myrs later (Angrand et al, 2018). This inherited thermal perturbation may have been present during the first 30-35 myrs of orogenesis (Angrand et al, 2018;Vacherat et al, 2014), maintaining temperatures during early orogenesis above the sensitivity limit of low-temperature thermochronometers (40-300°C; e.g., Carrapa, 2010;Peyton & Carrapa, 2013) and thus delaying any cooling record until the main Eocene collision .…”

“…On the other hand, the Aptian–Cenomanian rifting generated a major thermal pulse that had not reequilibrated before the onset of convergence some 10 myrs later (Angrand et al, ). This inherited thermal perturbation may have been present during the first 30–35 myrs of orogenesis (Angrand et al, ; Vacherat et al, ), maintaining temperatures during early orogenesis above the sensitivity limit of low‐temperature thermochronometers (40–300 °C; e.g., Carrapa, 2010; Peyton & Carrapa, ) and thus delaying any cooling record until the main Eocene collision (Vacherat et al, ). However, previous limited low‐temperature thermochronology data (Yelland, ) indicate that the massifs at the eastern end of the external Pyrenean orogenic system, Agly‐Salvezines, record a Campanian–Maastrichtian cooling signal, synchronous with the first period of accelerating subsidence in the retroforeland (Ford et al, ).…”

Formation of the Iberian‐European Convergent Plate Boundary Fault and Its Effect on Intraplate Deformation in Central Europe

“…In the following, we focus on the precollisional to early collisional evolution of the Pyrenees and summarize key information that provides insights into the tectonics around the onset of Africa‐Iberia‐Europe convergence. For further information on the Pyrenean orogeny we refer to the recent literature (Angrand et al, ; Grool et al, ; Labaume et al, ; Mouthereau et al, ; Teixell et al, ; Tugend et al, ; Vacherat et al, ).…”

Insights Into the Crustal‐Scale Dynamics of a Doubly Vergent Orogen From a Quantitative Analysis of Its Forelands: A Case Study of the Eastern Pyrenees

“…Black line indicates the trace of the ECORS Pyrenees deep seismic section shown in Figure b. Modified after Vergés et al () and Angrand et al (). (b) Interpretation of the ECORS Pyrenees deep seismic section, with major structural zones indicated.…”

“…Previous work proposes that the western Aquitaine Basin follows this predicted pattern (Desegaulx & Brunet, 1990;Naylor & Sinclair, 2008); however, more recent work shows that the eastern retro-foreland basin has a more complex history that challenges these models, including a temporary stagnation in subsidence for which the cause remains unclear Rougier et al, 2016). Vergés et al (2002) and Angrand et al (2018). (b) Interpretation of the ECORS Pyrenees deep seismic section, with major structural zones indicated.…”